In message <CAOtMX2g0TkQvM6N0yf_fr667XpAFupyY6auf8_8H6VJt7MqEkA@mail.gmail.c om> , Alan Somers writes: > On Sat, Sep 3, 2022 at 11:10 PM Konstantin Belousov <kostik...@gmail.com> wro > te: > > > > On Sat, Sep 03, 2022 at 10:19:12AM -0600, Alan Somers wrote: > > > Our /usr/include headers define a lot of symbols that are used by > > > critical utilities in the base system like ps and ifconfig, but aren't > > > stable across major releases. Since they aren't stable, utilities > > > built for older releases won't run correctly on newer ones. Would it > > > make sense to guard these symbols so they can't be used by programs in > > > the ports tree? There is some precedent for that, for example > > > _WANT_SOCKET and _WANT_MNTOPTNAMES. > > _WANT_SOCKET is clearly about exposing parts of the kernel definitions > > for userspace code that wants to dig into kernel structures. Similarly > > for _WANT_MNTOPTNAMES, but in fact this thing is quite stable. The > > definitions are guarded by additional defines not due to their instability, > > but because using them in userspace requires (much) more preparation from > > userspace environment, which is either not trivial (_WANT_SOCKET) or > > contradicts to standartized use of the header (_WANT_MNTOPTNAMES + > > sys/mount.h). > > > > > > > > I'm particular, I'm thinking about symbols like the following: > > > MINCORE_SUPER > > Why this symbol should be hidden? It is implementation-defined and > > intended to be exposed to userspace. All MINCORE_* not only MINCORE_SUPER > > are under BSD_VISIBLE braces, because POSIX does not define the symbols. > > Because it isn't stable. It changed for example in rev 847ab36bf22 > for 13.0. Programs using the older value (including virtually every > Rust program) won't work on 13.0 and later. > > > > > > TDF_* > > These symbols coming from non-standard header sys/proc.h. If userspace > > includes the header, it is already outside any formal standard, and I > > do not see a reason to make the implementation more convoluted there. > > > > > PRI_MAX* > > > PRI_MIN* > > > PI_*, PRIBIO, PVFS, etc > > > IFCAP_* > > These are all implementation-specific and come from non-standard headers, > > unless I am mistaken, then please correct me. > > > > > RLIM_NLIMITS > > > IFF_* > > Same. > > > > > *_MAXID > > This is too broad. > > I'm talking about symbols like IPV6CTL_MAXID, which record the size of > sysctl lists. Obviously, these symbols can't be stable, and probably > aren't useful outside of the base system. > > > > > > > > > Clearly delineating private symbols like this would ease the > > > maintenance burden on languages that rely on FFI, like Ruby and Rust. > > > FFI basically assumes that symbols once defined will never change. > > > > Why e.g. sys/proc.h is ever consumed by FFI wrappers? > > I should add a little detail. Rust uses FFI to access C functions, > and #define'd constants are redefined in the Rust bindings. For most > Rust programs, the build process doesn't check the contents of > /usr/include in any way. Instead, all of that stuff is hard-coded in > the Rust bindings. That makes cross-compiling a breeze! But it does > cause problems when the C library changes. Adding a new symbol, like > copy_file_range, isn't so bad. If your Rust program doesn't use it, > then the Rust binding will become an unused symbol and get eliminated > by the linker. If your Rust program does use it OTOH, then it will be > resolved by the dynamic linker at runtime - if you're running on > FreeBSD 13 or newer. Otherwise, your program will fail to run. A > bigger problem is with symbols that change. For example, the 64-bit > inode stuff. Rust programs still use a FreeBSD 11 ABI (we're working > on that). But other symbols change more frequently. Things like > PRI_MAX_REALTIME can change between any two releases. That creates a > big maintenance burden to keep track of them in the FFI bindings. And > they also aren't very useful in cross-compiled programs targeting a > FreeBSD 11 ABI. Instead, they really need to have bindings > automatically generated at build time. That's possible, but it's not > the default.
This is exactly what happened with DMD D. When 64-bit statfs was introduced all DMD D compiled programs failed to run and recompiling didn't help. The DMD upstream failed to understand the problem. Eventually the port had to be removed. > > So what the Rust community really needs is a way to know which symbols > will be stable across releases, and which might vary. Are you > suggesting that anything from a non-POSIX header file should be > considered variable? > Rust and every other community. -- Cheers, Cy Schubert <cy.schub...@cschubert.com> FreeBSD UNIX: <c...@freebsd.org> Web: http://www.FreeBSD.org NTP: <c...@nwtime.org> Web: https://nwtime.org e^(i*pi)+1=0
